WASHINGTON -- Damage to a silver-dollar-sized spot deep in the brain seems to wipe out the urge to smoke, a discovery that may shed important light on addiction.

The research was inspired by a stroke survivor who claimed he simply forgot his two-pack-a-day addiction -- no cravings, no nicotine patches, not even a conscious desire to quit.

"The quitting is like a light switch that went off," said Antoine Bechara of the University of Southern California, who scanned the brains of 69 smokers and ex-smokers to pinpoint the region involved.

The finding, reported in today's edition of the journal Science, points scientists toward new ways to develop antismoking aids by targeting the little-known brain region called the insula. And it sparked excitement among addiction specialists who expect the insula to play a key role in other addictions.

"It's a fantastic paper; it's a fantastic finding," said Nora Volkow, director of the National Institute on Drug Abuse and a longtime investigator of the brain's addiction pathways.

The study "shows unequivocally is the insula is a key structure in the brain for perceiving the urges to take the drug," urges that are "the backbone of the addiction," Dr. Volkow said.

The insula seems to be where the brain turns physical reactions into feelings -- like feeling anxious when your heart speeds up. When those reactions are caused by a particular substance, the insula may act as a sort of headquarters for cravings.

Some 44 million Americans smoke, and the government says more than 400,000 people a year die of smoking-related illnesses. Declines in smoking have slowed in recent years, making it unlikely that the U.S. will reach a public health goal of cutting the rate to 12% by 2010.

Nicotine is one of the most addictive substances known, and it is common for smokers to relapse repeatedly when they try to quit.

It isn't unusual for a health scare to prompt an attempt at quitting. "That's the quitting that's not as interesting," Dr. Bechara said.

If Dr. Bechara's findings are validated, they suggest that developing drugs that target the insula might help smokers quit. There are nicotine receptors in the insula, meaning it should be possible to create a nicotine-specific drug, Dr. Bechara said -- albeit years from now.

More immediately, Dr. Volkow of NIDA wants to try a different experiment: Scientists can temporarily alter function of certain brain regions with pulses of magnetic energy, called "transcranial magnetic stimulation." She wants to see if it's possible to focus such magnetic pulses on the insula, and thus verify its role.

Other neurologic functions are known to be involved with addiction, too, such as the brain's "reward" or pleasure pathways. The insula discovery doesn't contradict that work, but adds another layer to how addiction grips the brain, Dr. Bechara said.